Reciprocating piston pumps of the four ball variety have been known and used in industry for a number of years, particularly in automotive applications to pump paint in circulating systems. As noise regulations have become increasingly stringent in recent years, various proposals have been made to quiet the air motors which drive such pumps and great progress has been made in this area.
Once, however, the original source of noise (the air motor) was quieted, another source of noise became glaringly apparent, that of the steel check balls. The noise from these check balls alone can be on the order of 88 to 89 dbA.